In the electronics industry, the continuing goal has been to reduce the size of electronic devices such as camcorders and portable telephones while increasing performance and speed. Integrated circuit packages for complex systems typically are comprised of a multiplicity of interconnected integrated circuit chips. The integrated circuit chips usually are made from an integrated circuit material such as silicon or gallium arsenide. Integrated circuit devices are formed in various layers of the integrated circuit chips using photolithographic techniques. The integrated circuit chips may be mounted in packages that are then mounted on printed wiring boards.
Integrated circuit packages including integrated circuit chips typically have numerous leads, or lead fingers, that are attached and connected by solder or a variety of other known techniques to conductor patterns on the printed wiring board.
Typically, the packages on which these integrated circuit chips are mounted include a substrate or other chip mounting device. One example of such a substrate is a leadframe.
Leadframes also typically include at least an area on which an integrated circuit chip is mounted and a plurality of power, ground, and/or signal leads to which power, ground, and/or signal sites of the integrated circuit chip are electronically attached. Integrated chips may be attached to the leadframe using adhesive or any other techniques for attaching such chips to a leadframe which are commonly known to those skilled in the art, such as soldering. The power, ground and signal sites on the chip may then be electrically connected to selected power, ground and signal plane or individual leads of the leadframe.
Leadframes have been used extensively in the integrated circuit (IC) packaging industry mainly because of their low manufacturing cost and high reliability. Integrated circuit packages using leadframes remain a cost-effective solution for packaging integrated circuit chips, particularly with the introduction of various leadless packages in recent years.
Typical leadframe packages include a die attach paddle, or pad, surrounded by a number of leads. The leads may be temporarily attached to the die attach paddle by a number of tie bars. The die attach paddle also may be a heat sink to help remove the heat generated by the integrated circuit during operation away from the integrated circuit chip.
An integrated circuit chip, is attached to the die attach paddle using a conductive adhesive such as silver epoxy. A dam bar may be used to prevent the conductive adhesive from flowing off the die attach paddle. The conductive adhesive is cured after die attach. After the die is attached to the die paddle, a wire-bonding process is used to make electrical interconnections between the integrated circuit and the leads of the leadframe. After wire bonding, the leadframe with the integrated circuit chip attached is encapsulated using a molding compound and the tie bars are removed.
Such enclosures may include encapsulation in a plastic or a multi-part housing made of plastic ceramic, or metal. The enclosure protects the leadframe and the attached chip from physical, electrical, and/or chemical damage.
After the molding compound has cured, post mold curing and singulation steps are conducted to complete the packaging process. Solder balls are attached to the bottom of the leads to provide a means of connecting the integrated circuit chip to a circuit board. Alternatively, solder is plated onto the bottom surfaces of the leads to create the suitable stand-off height required for board mounting of the semiconductor package.
The leadframe and attached integrated circuit chip(s) may then be mounted on, for example, a circuit board, or card along with other leadframes or devices. The circuit board or card may then be incorporated into a wide variety of devices such as computers, automobiles, and appliances, among others.
One problem that persists with leadframes is that as the integrated circuits are subject to miniaturization requiring integrated circuit packages having higher numbers of leads in intricate designs often including isolated heat sinks additional tie bars and dam bars are needed to hold these intricate design features together during manufacturing of the integrated circuit package.
Additionally, coverlay tape may be applied to the leadframe to provide support for the integrated circuit package during the wire bonding and molding operations. However, the taping provides a cushioning effect that absorbs some of the ultrasonic energy transmitted during the wire bonding process resulting in defective wire bonding.
Attempts have been made to use leadframes without tie bars or dam bars, but have proven unsuccessful. One such attempt uses a leadframe having a base portion that is used to connect the die attach paddle to the number of leads. After the molding operation is performed the base portion is removed using a grinding process to disconnect the die attach paddle from the leads. The grinding operation, however, introduces potentially harmful stresses, which can have an adverse effect on the function and reliability of the integrated circuit package.
Also, these attempts have been unable to provide a stable bonding platform for hanging heat sinks or leads during the wire bonding process. Additionally, dam bars are often required across all leads to hold and arrange the leads in their peripheral or dedicated location. This has resulted in design limitations for tie bar and dambar insertion, and the need for larger unusable space in leadframe designs.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.